1. Field
The present disclosure relates to an electrolyte for a lithium secondary battery, and a lithium secondary battery including the electrolyte.
2. Description of the Related Art
Lithium ions batteries (“LIBs”) possess high energy density per unit weight and can be easily designed. Thus, these batteries have been developed for use in small electronic and portable IT devices. In recent years, small and medium sized lithium ion batteries have drawn attention as suitable power sources for electric vehicles and power storage devices storing electricity produced as an alternate.
A lithium secondary battery includes a cathode, an anode, and a separator. During discharging of the lithium secondary battery, oxidation reaction occurs in the anode due to deintercalation of lithium ions, while reduction reaction occurs in the cathode due to intercalation of lithium ions. The vice versa processes take place during the battery charging. The electrolyte has conductivity only for ions, not for electrons, and thus transfers lithium ions between the cathode and the anode.
Lithium ions intercalated into an electrode of a battery lead to charge neutrality with electrons entered into the electrode, and thus serve as media storing electric energy in the electrode. Accordingly, the quantity of electric energy storable by the battery is dependent upon the quantity of lithium ions intercalated into the electrode to create the charge neutrality. Although basic performance of the lithium secondary battery, such as operating voltage and energy density, is dependent upon the materials of the cathode and anode, the electrolyte also needs to have high-ion conductivity, electrochemical stability and thermal stability to ensure high performance of the lithium secondary battery.
A typical lithium ion battery electrolyte consists of a lithium salt and an organic solvent. The electrolyte needs to be electrochemically stable in a voltage range where reduction and oxidation proceed in the anode and cathode, respectively.
As the use of lithium secondary batteries is expanding to electric vehicles and power storage fields, electrode active materials for use at high voltages emerged and became available. Use of a relatively low-potential anode active material and a relatively high-potential cathode active material has led to a narrower potential window of the electrolyte, so that the electrolyte is more likely to decompose on a surface of the cathode/anode. Lithium secondary batteries for electric vehicles and power storage are likely to be exposed to external high-temperature environment conditions, and the temperatures of these lithium secondary batteries may rise during instantaneous charging and discharging. Accordingly, lifetime and stored energy quantity of the lithium secondary battery may be reduced in such high-temperature environment conditions.
Therefore, there remains a demand for the development of an electrolyte composition which would provide improved lifetime and high-rate characteristics of the lithium secondary batteries.